Stearic acid


Stearic acid
Stearic acid[1]
Identifiers
CAS number 57-11-4 YesY
PubChem 5281
DrugBank DB03193
ChEMBL CHEMBL46403 N
Jmol-3D images Image 1
Properties
Molecular formula C18H36O2
Molar mass 284.48 g mol−1
Appearance white solid
Density 0.847 g/cm3 at 70 °C
Melting point

69.6 °C, 343 K, 157 °F

Boiling point

383 °C, 656 K, 721 °F

Solubility in water 3 mg/L (20 °C)
Refractive index (nD) 1.4299
 N acid (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Stearic acid (first syllable pronounced either steer or stair) is the saturated fatty acid with an 18 carbon chain and has the IUPAC name octadecanoic acid. It is a waxy solid, and its chemical formula is CH3(CH2)16CO2H. Its name comes from the Greek word στέαρ "stéatos", which means tallow. The salts and esters of stearic acid are called stearates. Stearic acid is noteworthy as the most common saturated fatty acid, another common one being the C16 compound palmitic acid.

Contents

Production

It occurs in many animal and vegetable fats and oils, but it is more abundant in animal fat (up to 30%) than vegetable fat (typically <5%). The important exceptions are cocoa butter and shea butter where the stearic acid content (as a triglyceride) is 28–45%.[2]

Stearic acid is prepared by treating these fats and oils with water at a high pressure and temperature (above 200 °C), leading to the hydrolysis of triglycerides. The resulting mixture is then distilled.[3] Commercial stearic acid is often a mixture of stearic and palmitic acids, although purified stearic acid is available.

In terms of its biosynthesis, stearic acid is produced from carbohydrates via the fatty acid synthesis machinery via acetyl-CoA.

Uses

Generally applications of stearic acid exploit its bifunctional character, with a polar head group that can be attached to metal cations and a nonpolar chain that confers solubility in organic solvents. The combination leads to uses as a surfactant and softening agent. Stearic acid undergoes the typical reactions of saturated carboxylic acids, notably reduction to stearyl alcohol, and esterification with a range of alcohols.

Soaps, cosmetics, detergents

Stearic acid is mainly used in the production of detergents, soaps, and cosmetics such as shampoos and shaving cream products. Soaps are not made directly from stearic acid, but indirectly by saponification of triglycerides consisting of stearic acid esters. Esters of stearic acid with ethylene glycol, glycol stearate and glycol distearate, are used to produce a pearly effect in shampoos, soaps, and other cosmetic products. They are added to the product in molten form and allowed to crystallize under controlled conditions. Detergents are obtained from amides and quaternary alkylammonium derivatives of stearic acid.

Lubricants, softening and release agents

In view of the soft texture of the sodium salt, which is the main component of soap, other salts are also useful for their lubricating properties. Lithium stearate is an important component of grease. The stearate salts of zinc, calcium, cadmium, and lead are used to soften PVC. Stearic acid is used along with castor oil for preparing softeners in textile sizing. They are heated and mixed with caustic potash or caustic soda. Related salts are also commonly used as a release agents, e.g. in the production of automobile tires.

Niche uses

Being inexpensively available and chemically benign, stearic acid finds many niche applications. When making plaster castings from a plaster piece mold or waste mold and when making the mold from a shellacked clay original. In this use, powdered stearic acid is dissolved in water and the solution is brushed onto the surface to be parted after casting. This reacts with the calcium in the plaster to form a thin layer of calcium stearate which functions as a release agent. When reacted with zinc it forms zinc stearate which is used a lubricant for playing cards (fanning powder) to ensure a smooth motion when fanning. In compressed confections it is used as a lubricant to keep the tablet from sticking to the die.

Fatty acids are classic components of candle-making. Stearic acid is used along with simple sugar or corn syrup as a hardener in candies.

Stearic acid is used to produce dietary supplements.

In fireworks, stearic acid is often used to coat metal powders such as aluminium and iron. This prevents oxidation, allowing compositions to be stored for a longer period of time.

Stearic acid is a common lubricants during injection molding and pressing of ceramic powders.[4] It is also used as a mold release for foam latex that is baked in stone molds.

Metabolism

An isotope labeling study in humans[5] concluded that the fraction of dietary stearic acid oxidatively desaturated to oleic acid was 2.4 times higher than the fraction of palmitic acid analogously converted to palmitoleic acid. Also, stearic acid was less likely to be incorporated into cholesterol esters. In epidemiologic and clinical studies stearic acid was associated with lowered LDL cholesterol in comparison with other saturated fatty acids.[6] These findings may indicate that stearic acid is healthier than other saturated fatty acids.

See also

References

  1. ^ Susan Budavari, ed (1989). Merck Index (11th ed.). Rahway, New Jersey: Merck & Co., Inc. p. 8761. ISBN 9780911910285. 
  2. ^ Beare-Rogers, J.; Dieffenbacher, A.; Holm, J.V. (2001). "Lexicon of lipid nutrition (IUPAC Technical Report)". Pure and Applied Chemistry 73 (4): 685–744. doi:10.1351/pac200173040685. http://iupac.org/publications/pac/73/4/0685/. 
  3. ^ David J. Anneken, Sabine Both, Ralf Christoph, Georg Fieg, Udo Steinberner, Alfred Westfechtel "Fatty Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a10_245.pub2
  4. ^ Tsenga, Wenjea J.; Mo Liua, Dean; Hsub, Chung-King (1999). "Influence of stearic acid on suspension structure and green microstructure of injection-molded zirconia ceramics". Ceramics International 25 (2): 191–195. doi:10.1016/S0272-8842(98)00024-8. 
  5. ^ Emken, Edward A. (1994). "Metabolism of dietary stearic acid relative to other fatty acids in human subjects". American Journal of Clinical Nutrition 60 (6): 1023S–1028S. PMID 7977144. 
  6. ^ Hunter, J. Edward; Zhang, Jun; Kris-Etherton, Penny M. (January 2010). "Cardiovascular disease risk of dietary stearic acid compared with trans, other saturated, and unsaturated fatty acids: a systematic review". Am. J. Clinical Nutrition (American Society for Nutrition) 91 (1): 46–63. doi:10.3945/ajcn.2009.27661. ISSN 0002-9165. PMID 19939984. 

External links


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Look at other dictionaries:

  • Stearic acid — Stearic Ste*ar ic (st[ e]*[a^]r [i^]k), a. [Cf. F. st[ e]arique.] (Physiol. Chem.) Pertaining to, or obtained from, stearin or tallow; resembling tallow. [1913 Webster] {Stearic acid} (Chem.), a monobasic fatty acid, obtained in the form of white …   The Collaborative International Dictionary of English

  • stearic acid — n. 1. a colorless, odorless, waxlike fatty acid, CH3 (CH2) 16COOH, found in many animal and vegetable fats, and used in making candles, stearates, soaps, etc. 2. a commercial mixture of palmitic and stearic acids …   English World dictionary

  • stearic acid — Chem. a colorless, waxlike, sparingly water soluble, odorless solid, C18H36O2, the most common fatty acid, occurring as the glyceride in tallow and other animal fats and in some animal oils: used chiefly in the manufacture of soaps, stearates,… …   Universalium

  • stearic acid — stearino rūgštis statusas T sritis chemija formulė H(CH₂)₁₇COOH atitikmenys: angl. stearic acid rus. стеариновая кислота ryšiai: sinonimas – oktadekano rūgštis …   Chemijos terminų aiškinamasis žodynas

  • stearic acid — n Octadecanoic acid; one of the most abundant fatty acid s found in animal lipids; used in pharmaceutical preparations, ointments, soaps, and suppositories. * * * stea·ric acid stē .ar ik , .sti(ə)r ik n a white crystalline fatty acid C18H36O2… …   Medical dictionary

  • stearic acid — noun Etymology: French stéarique, from Greek stear hard fat Date: 1830 a white crystalline fatty acid C18H36O2 obtained by saponifying tallow or other hard fats containing stearin; also a commercial mixture of stearic and palmitic acids …   New Collegiate Dictionary

  • stearic acid — [ stɪərɪk, stɪ arɪk] noun Chemistry a solid saturated fatty acid obtained from animal or vegetable fats, used in making soap and candles. Origin C19: stearic from Fr. stéarique, from Gk stear tallow …   English new terms dictionary

  • stearic acid — noun a waxy saturated fatty acid; occurs widely as a glyceride in animal and vegetable fats • Syn: ↑octadecanoic acid • Hypernyms: ↑saturated fatty acid …   Useful english dictionary

  • stearic acid — noun a) The most common saturated fatty acid; it is found in all animal and most vegetable oils and fats; it is used in the manufacture of soap etc. b) octadecanoic acid, CH(CH)COOH …   Wiktionary

  • stearic acid — /stiˌærɪk ˈæsəd/ (say stee.arik asuhd) noun a colourless, odourless, insoluble, waxy, carboxylic acid, octadecanoic acid, C17H35–COOH, the glycerides of which are the principal components of animal fats …   Australian English dictionary


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